This invention relates to a laser beam machining system using a laser beam for cutting a workpiece and more particularly to an improvement in work failure at the work restart time after the work is interrupted.
FIG. 18 shows the configuration of a laser beam machine system. In a controller 1, a CPU (central processing unit) 2 reads a work program stored in a RAM 4 (random access memory) based on a control program stored in a ROM 3 (read-only memory) and controls the entire laser beam machining system. The RAM 4 stores work condition data, etc. in addition to the work programs. An I/O unit 5 converts a control signal output from the CPU 2 and sends the resultant control signal to a laser oscillator 6, which then performs emission, stopping, output change, etc., of a laser beam 7 in response to the received control signal. The laser beam 7 is sent via a mirror 8 to a laser beam machine 9.
The laser beam machine 9 is provided with a table to which a workpiece 10 is fixed and a work head 12 for irradiating the workpiece 10 with a laser beam. The laser beam 7 introduced into the work head 12 is gathered by a light gatherer disposed in the work head and is applied to the workpiece 10 through a nozzle 12a. At the same time, a work gas (not shown) is also sprayed to the workpiece through the nozzle. The laser beam machine 9 is provided with servo motors 13 and 14 for performing move control of the table 11 in two directions of X and Y axes. The servo motors 13 and 14 are connected to servo amplifiers 15 and 16 respectively in the controller 1 and are subjected to rotation control through the amplifiers in response to a control signal issued from the CPU 2. A move system in the Z axis direction for controlling the focus position of the laser beam applied to the workpiece 10 also exists, but here is omitted. Commands are given to the laser beam machining system and parameters are set for the system through a CRT/MDI unit 17.
FIG. 19 is a functional block diagram of the conventional laser beam machining system. The functions and configuration of the blocks will be discussed with reference to FIG. 19. In the controller 1, a program analysis section 18 analyzes the instruction contents of a work program and issues a command to a move command section 19 or a work condition command section 20. When receiving a work condition command from the program analysis section 18, the work condition command section 20 calls work condition data responsive to the command from a work condition registration section 21 and sets work conditions. If work condition values are specified directly in the program, the values are handled like the work condition data and the work conditions are set. The work condition data is data of piercing conditions, cutting conditions, etc., set in response to workpiece material and its plate thickness, such as laser output, duty, frequency, piercing time, etc., set as laser oscillator work conditions and speed set as a move condition of the laser beam machine for making a relative move of a workpiece with respect to a laser beam. If a move command is received from the program analysis section 18, the move command section 19 generates a travel distance from the work programmed path and setup work condition speed. An interrupt/restart determinating section 22 determines emergency stop to be caused by alarm occurrence, factitious temporary stop to be specified by a feed hold command, work restart to be specified by a work restart command such as the subsequent cycle start command, etc., and based on the determination, sends a stop/restart determination signal to the move command section 19 and the work condition command section 20. When receiving the stop/restart determination signal, the move command section 19 and the work condition command section 20 generate a move command and a work condition command and output them to the laser oscillator 6 and the laser beam machine 9.
FIG. 20A shows a work program example for the laser beam machining system and FIG. 20B shows a work process flow corresponding to the work program. The work operation will be discussed with reference to FIG. 20.
The program analysis section 18 analyzes the command on work program line N01 (piercing condition selection command) and outputs the piercing condition selection command. When receiving the piercing condition selection command, the work condition command section 20 calls piercing condition data stored in the work condition registration section 21 and sets piercing conditions at step S100 (the piercing is to make a hole at the work start time and the piercing condition data is laser output, duty, frequency, piercing time, etc.,). Likewise, the program analysis section 18 analyzes the command on work program line N02 (piercing execution command) and outputs the piercing execution command. Inputting the piercing execution command, the work condition command section 20 outputs a laser beam irradiation signal to the laser oscillator and waits for the piercing time set in the piercing conditions at step S101. Meanwhile, a through hole is made (completion of the piercing). Likewise, the program analysis section 18 analyzes the command on work program line N03 (cutting condition selection command) and outputs the cutting condition selection command. Inputting the cutting condition selection command, the work condition command section 20 calls cutting condition data and sets cutting conditions at step S102. Likewise, the program analysis section 18 analyzes the commands on work program lines N04 to N98 (move commands for moving the table in response to the cut shape) and outputs the move commands. Inputting the move commands, the move command section 18 drives the servo motors for moving the table at the speed set in the cutting conditions at step S103. As a result, the workpiece is cut to a desired shape. Subsequently, the program analysis section 18 analyzes the command on work program line N99 (cutting end command) and outputs the cutting end command. Inputting the cutting end command, the work condition command section 20 turns off the laser beam and work gas at step S104. Working of one workpiece is now complete.
If a temporary stop command is given due to alarm occurrence or by a feed hold command during the cutting following the program path (step S103), the interrupt/restart determinating section receives the temporary stop signal and outputs a work interrupt determination signal. When receiving the work interrupt determination signal, the move command section outputs a stop command for stopping the table move and the work condition command section outputs a stop command for stopping irradiation with the laser beam, spraying of the work gas, etc. Upon reception of the stop commands, the laser beam machining is stopped. Then, if a work continuation command is given by a cycle start command, the laser beam machining is restarted.
FIG. 21 shows a process flow at the work restart time. The operation at the restart time will be discussed with reference to FIG. 21. When a work restart command is given, the interrupt/restart determinating section receives the work restart command, determines work restart, and outputs a work start determination signal. Inputting the work start determination signal, the work condition command section restores the state required for the work gas spraying, laser beam irradiation, etc., to the state before the temporary stop (containing the work conditions) at step S105. Next, the move command section outputs a restart move command at step S106 and the cutting is restarted.
FIG. 22 is an illustration showing how laser cutting is performed. When cutting of the workpiece 10 by the laser beam 7 proceeds, a bottom face 10b of the workpiece 10 lags in the cutting progress behind a top face 10a (m shown in FIGS. 22 and 23). The thicker the workpiece and the faster the work speed, the more remarkable the tendency (as shown in FIG. 23). Therefore, if a temporary stop command is given during the cutting and the working is stopped, the top face of the workpiece is cut, but uncut portion m remains in the bottom face at the stop position. After this, if a work restart command is given in the state and the cutting is started in the same cutting conditions as before the stop, a flow of molten metal at the start time worsens because of the uncut portion m in the cutting restart part; work failure easily occurs.